RFR: 8268388: Update large pages information in Java manpage

[Thomas Stuefe]

On Wed, 9 Jun 2021 08:01:46 GMT, Stefan Johansson <sjohanss at openjdk.org> wrote:

> Please review this update to the text for large pages in the Java man page. 
> 
> The text for `LargePageSizeInBytes` was reviewed in this [CSR](https://bugs.openjdk.java.net/browse/JDK-8265517), and this change will integrate them into the actual man page. The *Large Pages* section further down in the man page was also a bit out-dated and have been brushed up a bit.

Hi Stefan,

just idle nitpicking, looks good otherwise.

Cheers, Thomas

src/java.base/share/man/java.1 line 5174:

> 5172: .RS
> 5173: .PP
> 5174: \f[CB]#\ echo\ 4096\ >\ /sys/kernel/mm/hugepages/hugepages\-2048kB/nr_hugepages\f[R]

- vm.nr_hugepages is not the only way to do this setup, since we have vm.nr_overcommit_hugepages, which are a bit more flexible to use. Is the java man page supposed to be complete in explaining this, or should it only show one possible way of many? 
- most users probably just use UseLargePages and are not aware of the different flavors. So they would not know what "explicit" means. How about, instead of mentioning UseSHM and UseHugeTLBFS, not just: "if you use large pages but don't use transparent huge pages (UseTransparentHugePages), large pages need to be preallocated...". 
- Otherwise, at least reverse the order of the two options? UseSHM is mentioned first, which is maybe historical, but TLBFS is the standard.

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PR: https://git.openjdk.java.net/jdk/pull/4425